To better understand the molecular basis of epidermal differentiation, and the structure and development of the integument generally, we study a variety of skin disorders to determine the underlying genetic error. This leads to hypotheses about the function of the causative gene in health and disease. Specific hereditary disorders are selected for study, and affected and unaffected members of many families evaluated clinically. A phenotypically homogeneous set of families is defined after careful clinical study. Gene localization methods (linkage analysis using candidate loci and/genome screening techniques) are used to identify the causative locus. Genomic organization is defined and a wide variety of mutation detection assays are used to define the spectrum of mutations in the disease. Goals include correlation of the molecular findings with the clinical presentation of the disorder to better understand the structure/function relationship of the gene expression in human tissues, and collaboration with cell biology and other laboratories with a mechanistic interest to determine the cellular sequelae of the gene mutation. In the past year we have identified mutations in erythrokeratodermia variabilis, a disorder involving anomalies of the epidermis and vascular system. The mutations we identified in connexin31 in EKV will allow progress in understanding the cellular communication. We have also identified a dominant mutation in connexin26 in hereditary deaf-mutism with palmoplantar keratoderma. We are testing several new methods, both manual and automated, for identifying mutations in the PTCH gene (the human homolog of Drosophila patched) in patients with Gorlin syndrome. These new methods will allow molecular diagnosis in a clinical setting. In addition, we have analyzed extensive clinical data on individuals with Gorlin syndrome and found some evidence for genotype/phenotype correlations. We are developing a rapid assay based on protein truncation for characterizing mutations in TGM1, the gene we defined recently as causing the severe autosomal recessive disorder, lamellar ichthyosis. We are continuing our analysis of families with ichthyosis vulgaris. In one large family, a histologic variable appears to co-segregate with genetic markers on chromosome 1q. In a second family, with a novel dominant ichthyosis, strong evidence of linkage to the epidermal differentiation complex has been found. We are currently sequencing candidate genes to search for mutations. A musculoskeletal disorder, autosomal recessive Kuskokwim syndrome, is also under study. We selected this disorder to test a method of DNA pooling in the laboratory. A complete genome screen using pooled DNA samples from 15 families and controls has been completed, and the chromosomal location of the KS gene has been This congenital arthrogyposis is found only in the Yupik Eskimos, and our results will now allow for carrier detection based on our identification of a carrier-associated haplotype in the population. Fifty individuals with severe cystic acne, treated at the NIH in the 1970's and 1980's have been contacted. We are continuing to collect family pedigrees and clinical data to define affection status and plan to test for genetic factors using the statistical technique of segregation analysis in the future. The approach we have chosen, detailed clinical and laboratory investigation of rare hereditary disorders, has been very fruitful in elucidating knowledge about the structure, function, and differentiation of the skin and related organ systems.